Cotton production in U.S. has undergone profound changes in the last two decades. For example, the successful eradication of the boll weevil and deployment of Bt-transgenic cotton have helped increase Georgia's cotton acreage from 125,000 acres in 1996 to more than 1 million acres. In addition, pest management advancements have helped reduce chemical insecticide applications from more than 15 per year in 1996 to less than 3 in 2007. However, the insect pest complex has also changed and previously unimportant insect pests like stink bugs now threaten productivity and fiber quality.
Stink bug damage to developing cotton bolls has recently been directly linked to decreased cotton fiber quality. Stink bugs damage developing cotton bolls by piercing the boll wall and feeding on the developing seed. In addition to physical damage to the seed (the fiber is part of the seed), pathogens may also be introduced during feeding or enter the boll through insect-induced wounds causing individual locks or the entire boll to rot and be unharvestable. Yield losses from bug damage to bolls have been documented in various studies (Cassidy & Barber (1939) J. Econ. Entomol. 32: 99-104; Toscano & Stern (1976) J. Econ. Entomol. 69: 53-56; Barbour et al., (1990) J. Econ. Entomol. 83: 842-845; Greene et al., (2001) J. Econ. Entomol. 94: 403-409). In no-choice feeding studies, stink bugs reduced seed cotton yield in bolls that had accumulated less than 550 heat units (Greene et al., (2001) J. Econ. Entomol. 94: 403-409; Willrich et al., (2004) J. Econ. Entomol. 97: 1928-1934). Relatively few studies have examined influences of boll feeding bugs on fiber quality (Toscano & Stern (1976) J. Econ. Entomol. 69: 53-56; Barbour et al., (1990) J. Econ. Entomol. 83: 842-845). Stink bugs prefer to feed on bolls ranging in age from 7-27 days after anthesis (Willrich et. al., (2004) J. Econ. Entomol. 97: 1928-1934), although some recent data show bolls only 3-4 days after white flower were most susceptible to shedding and stink bug injury. Cotton fibers develop to maturity within approximately 45 days of anthesis. Fiber elongation, measured as staple length, occurs during the first 3 weeks following anthesis, while fiber deposition or thickening, measured by micronaire, occurs during the second 3 weeks of boll development.
A number of phytophagous stink bugs, including the southern green stink bug, Nezara viridula, the green stink bug, Acrosternum hilare, and the brown stink bug, Euschistus servus have become serious pests of cotton production. These pests pose difficult management challenges because of limited information on basic ecology, distribution within fields and across the farmscape, and a lack of management tactics other than chemical control. There is also evidence that stink bugs are active flyers and frequently move among adjacent crops in the farmscape. Stink bugs have more than 200 known host plants (agronomic and nonagronomic plants).
Stink bugs are robust insects that use their piercing-sucking mouthparts to remove plant fluids from squares and bolls and can damage even relatively mature cotton bolls. Affected bolls then develop small sunken black spots on the outside surface. Internal evidence of feeding may be seen when bolls are opened by hand and lint, seeds, and carpel walls are examined for signs of feeding injury. The seeds and lint usually turn brown as a result of stink bug feeding. Wart-like callus growths may be present on internal carpel walls, marking the feeding wounds and the plant's response to injury.
Infestations are highly aggregated within a single field. A commonly employed method of determining if a crop field has a stink bug infestation involves the use of a drop cloth. Using this method, sample plants are vigorously shaken over a white cloth and the dislodged insects are enumerated. Typically, a few bolls are opened and inspected for signs of stained lint and internal injury. These methods, however, are time-consuming, may result in mechanical damage to the plants, and the drop-cloth method gives a count of the insects present, but not an indication of the extent of the damage to the plant tissues. Furthermore, development of cotton lint and seed damage may not be externally apparent even though the insects had pierced the boll. The grower may then incorrectly conclude that the crop was free of insect damage, allowing the pest to be untreated.